Can you place 5 nickels in space so that each touches the other 4. Itturnsout that there is a well known solution in the case of pennies, but itfails in the case of nickels. The critical height-diameter ration turns out (with the help of Mathematica) to be 12.47, and this ratio forpennies is 13 and for nickels 11. But there are other ways of doingnickels.

What about beer cans? Drinking straws? When is there a solution that doesnot have a triple or quadruple point (a point at which >2 cylindersmeet)?